I have recently installed a new heat sink & fan combination on my Core 2 Quad since my CPU was hitting about 70C under load. This has managed reduce temperatures while running Prime95 to about 54C, which I'm taking as a win (this is ~30 minutes after fitting).

I'm a little confused though. The temperature readings given above are for CORE temperatures, but HWMonitor is showing a 5th "CPU" temperature (4 temperatures being the individual core temps) which is showing 21C idle, when idle temperatures for the cores vary between 37C and 42C.

I guess there are two questions here:

1. Are my CPU/Core temperatures decent, and is it safe to overclock when these are stock clock temperatures?
2. I gather that the maximum safe operating temperature for a C2Q is ~70C, so which temperature should I measure against, the core temperatures (which are higher), or the CPU temperature reading?